Retorting process control



Sept. 26, 1961 G. D. cHEADLE RETORTING PROCESS CONTROL Filed Sept. 8, 1958 n W/ E E Q 0^ 0^ Uff L. 0A K .n nu wem, W L E M kk@ eww. A C U .nur HHH a m a EN FFW y KRD L Ha/Ov, WW@ f r/s o AM e .u A M am a M C f 73 f I/ Pla-550.25

an s Feaadf HYDlHdL/C FL wma/H a/ 0. M1 @fm om United States Patent 3,001,916 RETORTING PROCESS CONTROL George l). Cheadle, Long Beach, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed Sept. S, 1958, Ser. No. 759,705 Claims. (Cl. 202-6) ofsuch a process is shown in Berg U.S. Patent 2,501,153.

The shale solids are fed upwardly in sequence through a retort having a disengaging section and a kiln section each of which has the general shape of a vertical inverted truncated cone. Air of other oxygen-containing gas is introduced into the top of the retort and is passed downwardly therethrough. At the top of the kiln section, the air is preheated in an ash zone by contact with hot shale ash and passes to a combustion zone at a lower level where it supports the combustion of carbonaceous deposits on the educted shale. The llue gas produced by such burning passes downwardly to aneduction Zone at a lower level within the kiln section where it heats the shale and educts hydrocarbon oils and gases therefrom. The'mixture of educted hydrocarbons and ilue 'gas passes downwardly through a preheating zone in direct contact with the upwardly moving bed of raw cool shale, whereby the hydrocarbon oils are at least partially condensed and the raw shale is preheated in the lower part of the kiln section and the upper part of the disengaglng section. The hydrocarbons and flue gas then pass downwardly into the disengaging zone where the liquid and gaseous products are drawn off and separated from the upwardly moving shale. A solids-feeding mechanism located below the disengaging section is provided to `force shale upwardly through the retort. A selectively varied solids feed rate, as determined by the solids retorted, will maintain a more uniform retorting process. The invention concerns itself with a control method of how best to determine a condition of non-uniformity in the solids bed or change of elevation of the combustion zone of the process and how best to use the information so deter- Y mined to correct for the condition. l Y

Control of the process has heretofore been accompli'shed by changing the solids feed rate in response to changes in the differential pressure from the top of the kiln to the disengaging zone. An increase in differential pressure generallyindicates a lower elevation of the combustion zone with attendant bed slagging, plugging and some burning or partial oxidation of shale oil; and accordingly, an increase in differential pressure was used to increase the solids feed rate, and vice versa. Such pressure differentials provide a rapid response control, but since the dilferential pressure could also vary with other factors such as particle size or horizontal uniformity, it

could provide a false indication that shale feed rate Fice ture of the kiln wal-1 at one side of the kiln section,but in general it has been found that this does not respond as well as differential pressure control to variations from horizontal of the combustion zone, nor does it appear to," be as rapidly responsive as differential pressure control;

It is an object of this invention to provide a control method for a solids upow retorting process in whichV cyclic rising and falling of burning zone elevation within the solids of the retorting process is substantially eliminated. y

It is a further object to providesuch a control method as in the foregoing object in which process zones are maintained at substantially constan-t levels irrespective of chance variations in solids consist which temporarily. changes the permeability of the up-ow solids bed to' downward uid passage.

It is also an object of this invention to provide ,an` optional combination method comprising the method for' attaining the foregoing objects in combination with a dif-A ferential pressure process control method.

The invention is carried out by a method of control in which an average Ytemperature indication, obtained from one, or preferably several, spaced moving temperature samplers of the upflowing solids at the surface of the ash bed, is used to control the solidsfeed rate. Theset samplers are preferably thermocouples connected elec trically in parallel and attached to one or more of the Scrapers removing ash from the top of the bed. The'l average temperature indication is preferably used tomodulate the fast responding differential pressure control of the feed rateV as described above, but it may alsoserve to control shale feed rate directly without use of" ditferential pressure control. f

Preferable forms of the invention include a retorting process having a frusto-conical ash bed with tempera-l ture samplers conveniently moved in ahorizontal rotary motion attached within 10 to 90 percent radial locations' to an ash bed scraping means.l The method of temperature control including the inventive concept in its most basic form comprises control of solids feed rate to in-` crease solids feed rate with properly selected temperatureA indications decreasing from a normal process indication; and decreasing solids feed rate with the temperature indications increasing from a normal process indication.;v All forms of the control method include controlled up-l ward solids feed rate, temperature sampling above a com-f bution zone, and an inverse relationship between magali" tude of sampled temperature and magnitude of feed rateof the upwardly fed solids.

The method is conveniently illustrated and described f, by reference to the drawing in which: f

FIGURE l illustrates schematically the method v of the invention as applied to an oil shale retort; and

FIGURE 2 shows in a fragmentary cross section view,I the detail of attachment of a typical thermocouple to a scraper blade. l As shown in FIGURE l, the retort com-prises a kiln section l17 and a disengaging section 20, both lled with solids. 'Ihe upper layer of solids comprises a preheatingff zon-e 15 wherein incoming air is heated by heat exchange against hot shale ash. Immediately below the preheating zone 15 is burning zone 16 wherein the preheated airl' burns carbonaceous material from the educted shalegandi below this is eduction zone 18 wherein the hydrocarbons.`i are educted from the shale by the downwardly mow'ng stream of hot flue gas produced in burning zone 16..'i

^ j Next below is shale preheating or fluid coo-ling zone 19 wherein the hot mixture of educted hydrocarbons and flue gas is cooled and partially condensed by heat exchange against the raw shale.

' Disen-gaging section 20 is equipped with openings 32` of smaller size than the shale, through which the liquids.

and gases may ow, thus lforming a separation zone 21 wherein these uid products are separated from the shale solids and pass into separator-settler 33 as described below.

At one side of disengaging section is hopper 28 into which the raw shale is charged, and below disengaging section 20 is the solids-feeding mechanism which comprises a reciprocating feeder piston 22 enclosed within a feeder housing 23. Feeder piston 22 is contained Within feeder cylinder 24 mounted on trunnion 25.Y Hyd'raulic actuating cylinder 26 disposed within cylinder 24 vertically reciprocates piston 22 in feeder cylinder 24. A second actuating hydraulic cylinder 27 positioned withinfeeder housing 23 permits feeder cylinder 24 to be placed in communication either with the lower opening in disengaging section 20 or Iwith the outlet of shale feed hopper 28. This operation of cylinders 26 and 27 is conventional, being indicated schematically by use of valves 101 and 102 in the hydraulic fluid feed lines. Uliston 22 is shown as having just completed forcing a charge of shale upwardly into the retort proper. In the succeeding cycle of operation, actuating piston of cylinder 27 is retracted to draw feeder cylinder 24 into communication with hopper 2S. Actuating piston' of cylinder 26 is then operated to draw piston 22 into its lowermost position, thereby allowing feeder cylinder 24 to ll with shale yfrom hopper 28. Actuating cylinder 27l is then extended to return feeder cylinder 24 to the vertical position shown, and actuating cylinder 26 is then extended to raise piston 22 and force the shale charge upwardly into the retort. This cycle of operations automatically repeated continuously by use of conventional hydraulically operated valves controlling the paths of the hydraulic iluid, thereby feeding raw shale into the bottom of the retort and displacing hot spent shale ash from the top thereof. Hydraulic fluid owto both cylinders 26 and 27 through line 87 is controlled by servo-control 83 interconnected by mechanical means 84 to control variable delivery pump 85 having fluid source 86, and this serves to control the rate at which the shale is fed through the retort.

Surrounding disengaging section 20 is separator-settler 33in which a liquid level as indicated is maintained. The liquid is drawn o through line 34 and the gas through line 35. Compressor 36 serves to create sulicient vacuum in vessel 33 to draw air into the top of the kiln and draw the fluid products as described down through the retort. Since the top of the kiln and the sale feed hopper are both open to the atmosphere, this vacuum or diierential pressure magnitude can be measured by the difference in liquid level in separator 33 and hopper 28, as shown, or by direct measurement of the vacuum in the vapor space of. separator 33 as signaled by transmitter 80, which is a dilerential pressure cell.

At the top of the retort is a hood 37 having `a spout 29 which provides entry for air to the top ofl the kiln and exit for hot spent shale. This hot spent shale is scraped from the upper surface 12 of ash zone 15 byV three Scrapers 51 which are rotated about the vertical axis of the retort by means of drive table 54. Attached to each scraper blade is a shoe 52 containing a thermocouple 50. The two leads 53 (shown as one) from each thermocouple, which measure temperatures T1, T2, and T3, respectively, are connected in parallel at point 57 to yform a single pair of leads 68 which Ahave a potential difference which is the average of the three pairs and indicates the average temperature TA.

In manual operation, the operator simply notes the average temperature TA by suitable measuring means and adjusts delivery of pump 8S to maintain TA at the desired value or set point. This is termed direct temperature control. Preferably, however, the control should be according to both average temperature and pressure difference, a form of control which is described below as cascade operation, where it is carried out automatically,

According to this type of control, if the differential pressure remains constant at the desired point or set point, and the temperature rises, indicating too high a combustion zone, the operator would reduce the feed rate by an amount which he would estimate would restore the combustion zone to its proper level. lf at the same time that the temperature rose, the magnitude of differential pressure, or vacuum, also dropped (the latter also indicating too high a combustion zone) the operator would reduce the feed ratev even to a greater extent, until the dilerential pressure was restored to normal. If, however, the temperature rose, but at the same time the diterential pressure rose (these being contradictory symp toms) the operator would wait until one or the other became normalized. For a reduction in temperature, the converse controls indicated above would apply.

Control unit 71 of FIGURE 1 serves to carry out the above manual controls automatically. Referring to FIG URE l, the electricalenergy of leads 68 is changed to a corresponding amount of air pressure in line 74 by an electrical to air transducer 72, the air being supplied through conduit 73. The transducer 72 is set to vary the pressure of air in the outlet 74 from an established minimum for a minimum expected temperature to an establishedV maximum for a maximum expected temperature. The air pressure signal in line 74 is sent to temperature recorder-controller 7S which records the temperature and also gives an output air pressure in line 76 for cascade control which varies directly with pressure in line 74 but has sutlicient power to control servo-control 83.

-If it is desired to control the shale feed rate directly according to TA, valve 140 to by-pass conduit 144 and valve 142 to pressure set' panel 7,8 are set so as to direct the air signal of recorder-controller to a position control servo-control 83 so as to adjust its setting for control of variable delivery hydraulic pump 8S. FIGURE l also shows inter-control mechanical linkage means 84 and hydraulic fluid supply conduit 86 to pump 85. The set point of controller 7S is set for the desired temperature, and it automatically controls the solids feed rate to maintain this temperature.

In the preferred method of control however, valve 140 is closed and valve 142 is open so that the air signal from recorder-controller 75 for `the temperature signal indication is used to modulate another control, namely, a dierential pressure controller 77, through a set panel 78. This is done as follows: The differential pressure transmitter 30 serves to convert the pressure in line 81 to an inverse tluctuating pressure in line 81a sufficient to drive controller unit 77. The'latter comprises controller 79 and set panel 78. The output air from controller 79 goes to servo-control 83 via lines 82 and 144 to control the variable delivery pump and solids feed rate. If the temperature control were `not used at all, controller 79 would be set to maintain the-desired differential pressure by adjustment of servo-control y83. In the cascade method of control, however, the set point (or desired differential pressure) of controller 79 is set by the signal action of controller 75 through control panel 78 in accordance with the average temperature TA.

Thus, for example, if TA were to remain constant at the desired temperature or set point, such as l-lOO F., and the' desired diierential pressure, or vacuum, were of a magnitude of 20" of water, controller 79 would serve to increase the solids feed rate if the differential pressure, or vacuum, became more than 20, and to decrease the solids feed rate if the dierential pressure dropped below 20". Similarly, if the differential pressure were to remain constant at the desired 20" value, and the average temperature were to increase above 1100 F., the controller 75 would serve to change the set point of controller 79 so as to make the latter respond as if the differential pressure, or vacuum, had become less (i.e., decrease Vthe feed rate); or if the average temperature dropped below l F., the controller 75 would reset.

sperare theset point of ycontroller' f79 to make the latter behave asif the dierential pressure, or vacuum, had increasedl (i.e., increase the feed rate). If both the average temperature and the differential pressure were to depart from the desired set points, the feed rate might be maintained constant (in the event .the increase in temperature` offset the increase in dierential pressure) or might be changed at an` accelerated rate (in the event the increase in temperature were to be accompanied by a decrease in difterential pressure, as in the normal operation).

It will be noted that in the above system, the temperature controller 75 is used as Athe master controller,v and the differential pressure controller 79 is used as the secondary controller. This is the preferred modilication, although the converse may also be used. In the converse system the control set panel 78 would be utilized in conjunction with controller 75 rather than controller 79; 79 would be used as the master controller, its output going through set panel 7S to modulate the set point to secondary controller 75; and the output of- 75 would control servo-control 83.

It may be noted that in cascade operations there isanv inverse relationship between temperature magnitude and differential pressure, or vacuum, magnitude. An increase in -temperature indicates a rrise in the position of the combustion zone, whereas a greater vacuum, or diierential pressure, indicates a lowering of the combustion zone. The automatic controllers must therefore be set to cornpensate for this.

.Briey, the operation of the equipment is as follows where a high combustion zone is assumed, With valves 140and 14Zfnclosed there is a decrease in the amount ofvacuum, or differential pressure. Since the vacuum is less, theabsolute pressure increases or-moves closer to atmospheric pressure inline 81. Pressure in -linelz decreases which is` inverse to line 81 pressure. Pressure in line `S2 also decreases in direct relationship with line 81av pressure, andthe rate of-uiddelivery-of pump 8S also decrea se s. With valve 1'40 open and valt/e142 closed an increase in temperature TA increases air pressure inline-74. Pressure in line Mli-decreases in inverse relationship with line 74 pressure, and the rate of tiuid delivery of pump v55 also decreases With valve -140 closed and 142 open there iscascade control andan increase in temperature TA increases air pressure in line 74. Controller 75-is now set differently, however, such that pressure in line 76 increases in direct relationship with line 74 pressure. Assuming for the moment that differential pressure remains unchanged, the effect of increase in pressure of line 76 resets the index of secondary controller 79 such that an unchangeddifferential pressure'signal acts to cause a pressure-decrease in line 82.` This results since the unchanged normal signal in line 81a acts as if it were low with respecttothe higher index. `Thus pressure in line 82 is decreased, and the rate of uid delivery of pump 8'5 also decreases;

OConverse operation, in the above instances, would of course take place where a low combustion zone is assumed. e

FIGURE 2 shows in detail a cross section. of the steel shoe 52 schematicallypresented in FIGURE l View, in'

which one of thethermocouples Si) has its hot junction 'responsivev to temperature inserted and held within a4 hole.4t) in the shoe between a'plug 42 and the scraper. The Vplug 42 -is held in place by a weld 44 `and the shoe is held'to the scraper 51 by welds such as 46. Leads 53 aresuitably'- insulated and pass to protective conduits (not shown)'throutgh a slot 48 in the shoe '52. The shoe,

suchas A52,which holds a thermocouple in `place iS preferably positioned as lclose as possible to the ash bed surface 12 on the trailing side of the rotating scraper 517. The front surface of a scraper Yblade would also be a satisfactory location in most instances. With such a shoe SZinset, so as to be level with the leading or forward Scraper surface, this would also be a satisfactory arrangement as then a smooth forward scraping surface'would be provided.

As a specific example of the invention, the retort corn'-4 prises a kiln section and a disengaging section, each in the form of an inverted truncated cone, the kiln being 12 feet high and having a l7foot upper diameter andl 15.2-foot lower diameter, and the disengaging section being 13 feet high and having a 51/2-foot diameter feed piston at its entrance. The fed piston is driven hydrauli- Y cally as illustrated in FIGURE 1, the hydraulic pump 35 being controlled by apposition control motor valve 8 3: which is Conomotor model B-51XB-A manufactured by' Conoilow Corporation of Los Angeles. At the top of the kiln there are three straight sloping scraper blades uniformly distributed around the periphery of the kiln,

the outer ends of these blades being about l4 inches fromthe top rim of the kiln and the blades extending radially inwardly at an angle of about 40 with the horizontal toradial location of a horizontal scraper extending out- Brown model 158N32PS manufactured by Minneapolis--l Honeywell Regulator Company of Philadelphia. ,The output of this transducer is sent tocontroller 75, a model 54/58 manufactured by the Foxboro Co. of Foxboro,

Massachusetts. The output of controller 75 *is sent tothe air pressure set panel 78,-jwhich is a model M/57SR also manufactured by the Foxboro Company; and. the;

output of set panel 78 goes to controller 79, which is also a model 54/58 manufactured by the Foxboro Corn-' pany. The output of controller 79 is sent to Conomotor servo-control 33 previously described. The input to controller 79 is the output from transmitter 80, which is a model 13A differential pressure-cell manufactured by the4 Foxboro Company; and the input to transmitter Sil is the conduit connecting it to the vapor space of the separator.-

operate on a 3 to l5` settler 33. All these instruments p.s.i.g. air supply.

In operating the above retortvat anaveragerate'. .off

about 975 tous per day of Coloradofshale having'a Fischer assay of about 35 gallons per ton, the tempera.

ture controller 73 was set to maintain a temperature of 1075 F., and the set point of controller '79 at 28 inchesf of water differential pressure, when the temperature was The units were connected vas de-v scribed above so that an increase in average temperature,

at the desired point.

and/ or a decrease in vacuum or differential pressure vmagnitude, caused a decreased solids feed rate.

the kiln at a' rate of about 4 revolutionsv perv hour.

In the above example, the controllers 75 and 79 were so adjusted that a change of F. in the average. terny perature would cause about the same change insolids4 feed rate as a 5.5inch (water) change in differential pressure. l'

It was found that with the above controls, unusually uniform operation was obtained, as compared with-the usual control, which employed no temperature control? but exclusively used differential pressure control of the feed rate.

Although the above is an operable example `of the i invention, it is not to be considered as limiting.. lt is not necessary that three thermocouples be used, or that the thermocouples be attached to scraper blades ormoved'- 'One orV in rotation about the central axis of the kiln. more thermocouples may be used, providing that a representative average temperature of the upper surface of the ash bed is obtained. Thus one thermocouple may be moved across the surface of the bed in such a fashionV as to obtain an average temperature; or a relatively large The scraperi blades were rotated around theA centralr vertical axis of- Y typical temperatures of the combustion zone.

number of non-moving thermocouples may be stationed at suitable points distributed across the surface so as to give an average temperature which is representative. Preferably, however, more than one therrnocouple is employed and each thermocouple is moved across a representative area of the surface of the bed. Generally speaking the representative surface comprises the surface covered by 10-90 percent of the radius of the kiln about its central axis.

It is also noted that in FIGURE l the scrapers are designed to permit a buildup of the solids above the top level of the kiln. This is a preferred arrangement, since it permits maintaining a substantial portion of the combustion zone above the top of the kiln. However, the invention is operable with dat Scrapers, reciprocating Scrapers, or scrapers of spiral shape or any other Scrapers which serve to maintain the upper surface of the bed n its desired position and shape. The thermocouples are pref erably attached to the scraper blades, but as previously indicated, may be independent. The thermocouples or other temperature sensing means must be adapted to sense the average temperature of a representative area of the upper surface of the ash bed.

`Temperature indications satisfactory for controlling the oil shale retort have been found to occur at the top of' the described retort. Optimum temperatures for the ternperature sensing will be determined by the best process condition. These temperature indications are taken in the oil shale ash residue at the retort top above the combustion zone at a level wherein the ash temperature is substantially constant at some values above 1000" F. and below 1500 F. Preferably the temperature will be substantially constant, for example, 1.075 F., within a temperature range'of 1050" F. to 1100 F. It is preferred that the indicating temperature range is not selected above 1500 `F., or more as found in the combustion zone where such higher temperatures exist, since such sampling does not provide as reliable control because of the possibility of greater frequency `of nonash temperatures 4below 1000 F., taken further along in the ash discharge path, will as a rule be too remote to provide goed reliable information as to what is happening in the retorting process at such an instant.

Briefly, then, the invention comprises the method of use of average ash temperature indications to control feed rate to a solids updiow oil shale combustion process retort as a means of process control within such a retort. The invention also comprises the method of combining such foregoing temperature control with differential pressure control of. shale feed rate as a process control within such a retort. The method of obtaining the average temperature indication comprises use of one moving thermocouple, or more than one thermocouple or other temperature sensing means spaced, when comprising a plurality of elements, from one another in a selected pattern and moved over the upper surface of the retort at the ash bed surface. Preferably, the movement of thermocouples is carried out as a rotation at the same speed of rotating ash Scrapers for such a solids upiiow retort.

The temperature control method disclosed results in smoother operation of the solids uptiow process in which the burning zone location is held at substantially a constant depth, both for the temperature control method as such, and for the method combining temperature control with differential pressure control. Temporary changes in solids consist and content cause no sudden changes in process control as experienced solely with differential pressure control resulting from the rapid differential pressure changes. Such solids consist changes affect process control only more gradually as the retorting process indicates substantial change in an average temperature which is measured. The foregoing advantages realized by the control method of the invention result in a more uniform process which, because of closer control,

Indicating requires smaller peak. capacity design of retorting apparatus. Thus, because the retorting apparatus may be oper-` ated constantly' at near peak capacity, there is an appre ciable commercial advantage gained over similar retorting. apparatus not so controlled. In addition the closer control of this invention will reduce operating costs by adaptability to centralized control of several retorts, since non-uniform cyclic and overresponsive retorting process control is substantially avoided.

It is to be understood that the method comprising the invention as discussed above and as shown by the drawings is illustrative only, and that the invention is not to belimited except in accordance with the following claims which define the invention.

I claim:

1. In a process for retorting -solids in which said solids are fed upwardly and successively as a compact bed through a combustion zone and an ash cooling zone, and in which oxygen is passed downwardly through said ash cooling zone into said combustion zone, the improvc' ment which comprises measuring the `average temperature of the upper surface of the ash cooling zone, and varying the upward solids feed inversely with the variation of average temperature so measured.

2. A process as defined in claim 1 wherein said average measurement of temperature is obtained by moving at least one temperature sensing means yacross a representative portion of said ash surface.

3. A process as defined by claim 2 wherein said average measurement of temperature is obtained from a plurality of electrical temperature sensing means connected electrically to provide an average temperature signal indication.

4. A process as defined in claim l wherein ash is scraped from said upper surface by rotating at least `one scraper horizontally about the axis of the ash cooling zone.

5. A process as defined in claim 4 wherein the average temperature is measured by a plurality of temperature sensing means which are spaced along said scraper at positions' between 10 percent and 90 percent from the `axis of said retort.

6. A process as defined in claim 4 wherein a plurality of scrapers symmetrically arranged is used and each of said Scrapers carries a temperature sensing means located at la position substantially equal in radial distance from` the axis of said retort.

i7. A process as deiined in claim 6 wherein the Scrapers are shaped and positioned so as to form the ash surface into 'a substantially frusto-conical shape.

8. A process as defined in claim 1 wherein said solids fed upwardly comprise oil shale particles subjected to said combustion within the process.

9. In a process for retorting shale in which shale solids are fed upwardly and successively as a compact bed through a preheating zone, a retorting zone, a combostion zone and an ash cooling zone, and in which uids are passed downwardly through said zones in reverse order, the improvement which comprises: measuring the average temperature of the upper surface of the ash cooling zone, measuring the amount of differential pressure from the top of the ash cooling zone to the bottom of the shale preheating zone, and varying the rate of upward solids feed inversely with the variation of said average temperature and directly with variation of said amount of differential pressure.

10. A process as defined in claim 9 wherein said ash is scraped from said upper surface by rotating at least one scraper horizontally about the axis of the ash cool; ing zone, and wherein said average measurement of temperature is obtained by attaching at least one temperature sensing means to said scraper.

11. A process as defined in claim 10 wherein saidscraper is shaped and positioned so as to form the 'ash surface into a substantiallyfrustoconical shape and the average temperature is kept substantially constant at a value above 1000 F. and below 1500 F.

12. An apparatus for retorting shale which comprises a vertical kiln, feeding means for moving a compact bed of shale upwardly through said kiln, scraper means above said retort for maintaining a uniform ash bed surface at the top of said bed of shale, temperature sensing means adapted to measure the average temperature of said surface, and means for varying the rate of operation of said feeding means inversely with the change in temperature sensed by said temperature sensing means.

13. Apparatus for measuring temperature variation in a process for retorting solids in which said solids are fed upwardly and successively as a compact bed through a retort having `a combustion zone and an ash cooling zone, said apparatus for measuring comprising: at least one movable ash scraping means for removing ash by substantially horizontal movement over solids of the ash -cooling zone, in combination with at least one temperature sensing means attached to said movable ash scraper for sensing representative temperature over the surface of said ash zone, whereby said temperature sensing means may be used to control upward solids feed rate inversely with the variation of temperature sensed relative to an optimum temperature value selected for the process at the temperature sensing location.

14. Apparatus according to claim 13 wherein said ash scraping means comprises a movable scraper horizontally rotatable about the axis of said ash cooling zone.

15. Apparatus according to claim 13 wherein said substantially horizontally moving scraping means is shaped with descending bllade portions adjacent the retort edge which are positioned so as to rotatably form the ash surface into a substantially frusto-conical shape.

16. Apparatus for measuring as dened in claim 13 wherein said scraping means comprises a plurality of scrapers symmetrically arranged about an ash zone central axis and having each of said scrapers carrying a temperature sensing means located thereon equal in radial distances from said axis.

17. Apparatus for retorting shale to form carbonaceous shale and burning said carbonaceous shale to form shale ash, which comprises feeding means for passing said shale as a compact bed upwardly through a retort and successively through a retorting zone and a combustion zone therein, and an ash cooling zone above said combustion zone, means for passing oxygen downwardly through said ash cooling zone into the combustion zone of said retort, at least one movable ash scraping means for removing ash by substantial-ly horizontal movement over solids of the ash cooling zone, in combination with at least one temperature sensing means attached to said movable ash scraper for sensing representative temperature over the surface of said ash zone, means for sensing amount of diierential pressure from a point above said ash Icooling zone to a point below said retorting zone, and means for varying the rate of operation of said feeding means cumulatively, inversely with the average temperature sensed, and directly with the amount of dilerential pressure so measured.

18. Apparatus for measuring as defined in claim 17 wherein said substantially horizontal moving scraping means is shaped with descending blade portions adjacent the retort edge which are positioned so as to rotatably form the ash surface into a substantially frusto-conical shape.

19. Apparatus for measuring representative variation in a process as delined in claim 17 wherein said temperature sensing means comprises a plurality of electrical temperature sensing means connected electrically to provide an average temperature signal indication at the horizontal location of said temperature sensing means.

20. Apparatus for-measuring as defined in claim 17 wherein said scraping `means comprises a plurality of scrapers symmetrically arranged about an ash zone central axis land having .each of said scrapers carrying a ternperature sensing means .located thereon equal in radial distances from said axis.

References Cited in the tile of this patent UNITED STATES PATENTS 2,606,863 Rehbein Allg. 12, 1952 2,640,019 Berg May 26, 1953 2,725,351 Grote Nov. 29, 1955 2,816,858 Walker Dec. 17, 1957 2,904,518 Shea Sept. 15, 1959 

1. IN A PROCESS FOR RETORTING SOLIDS IN WHICH SAID SOLIDS ARE FED UPWARDLY AND SUCCESSIVELY AS A COMPACT BED THROUGH A COMBUSTION ZONE AND AN ASH COOLING ZONE, AND IN WHICH OXYGEN IS PASSED DOWNWARDLY THROUGH SAID ASH COOLING ZONE INTO SAID COMBUSTION ZONE, THE IMPROVEMENT WHICH COMPRISES MEASURING THE AVERAGE TEMPERATURE OF THE UPPER SURFACE OF THE ASH COOLING ZONE, AND VARYING THE UPWARD SOLIDS FEED INVERSELY WITH THE VARIATION OF AVERAGE TEMPERATURE SO MEASURED. 